A typical multiple-input-multiple-output (MIMO) network comprises a base transceiver station (BTS) with an antenna array and multiple mobile stations (MSs), at least one of which has multiple antennas. It has been demonstrated that employing a beamforming technique can enhance the performance of an MIMO network. Therefore, the beamforming technique has been adopted by several wireless communications standards, such as IEEE 802.16 d/e (WiMAX)
In an MIMO network employing a beamforming technique, a BTS and an MS rely on beamformed signals to communicate with each other. The signals transmitted from the multiple antennas on the BTS are weighted based on phase and magnitude. The BTS computes beamforming weighting vectors for a receiver of a wireless communications network according to channel condition. Subsequently, the beamforming weighting vectors are applied to the multiple antennas on the BTS to de-correlate transmitting signals on the beamformed channels.
The performance of a wireless communications network is often evaluated based on its capacity and throughput. One of the factors that impact network performance is that the transmitter of a message has the exact information about the channel condition between the transmitter and the receiver. More specifically, whether employing a beamforming technique will result in optimal network performance depends on the accuracy of the channel condition that the transmitter obtains.
Although the combination of beamforming and MIMO techniques further improves network performance, the data transmitted via a wireless channel may still be corrupted due to unexpected impairment of the channel condition. To deal with this issue, a technique of re-transmission, e.g. automatic repeat request (ARQ), is used. The ARQ is a conventional scheme in which a wireless receiver requests re-transmission of a data sequence when unrecoverable frame errors are detected at the receiving end. The most commonly used error detecting code is the cyclic redundancy check (CRC) code.
A data sequence can be protected by an error correcting code, which increases the probability of a successful transmission. An ARQ scheme that combines the ARQ principle with error correcting code is known as a hybrid ARQ (HARQ) scheme. In a conventional HARQ scheme, the re-transmitted data sequence is encoded exactly the same way as the first transmission.
The wireless receiver combines the re-transmitted data sequence with the previously received one and then decodes the combined data sequence. As a result, the re-transmitted data sequence, which is subject to the same channel condition as the original transmission, suffers from the same type of unrecoverable error. The conventional HARQ algorithm only provides limited improvement to the performance of the system.
As such what is desired is method for re-transmitting a data sequence using a different encoding method to avoid unrecoverable errors in a wireless communications network.